The term thermal analysis may encompass various measurement methods, including inter alia, calorimetry, DSC (differential scanning calorimetry), TGA (thermo-gravimetric analysis), determination of a dielectric constant and also combinations of these methods.
The implementation of these methods on, with or by means of a suitable sensor, in particular a MEMS-based sensor (MEMS: Micro-Electro-Mechanical Systems), is particularly advantageous for the analysis of small samples or extreme thermal processes. Small samples are here understood as samples with dimensions in the sub-millimeter range and weights in the microgram and nanogram range.
A sensor in accordance with the invention is preferably a MEMS sensor, which includes an integrated circuit and which is configured in such a manner that a thermal analytical measurement can be carried out on a sample with or on this sensor. Preferably, this is a DSC or TGA-MEMS sensor, a MEMS sensor for the determination of the dielectric constant or a combination thereof, by use of which at least one thermal analytical property of a sample arranged on the sensor or associated with the sensor can be determined. It is possible to differentiate between active and passive sensors, an active sensor having active components, such as for example heating resistors, and a passive sensor for example being subjected to a temperature program by means of an external temperature control unit. Such sensors comprise at least one measuring position for a sample, but can also comprise a plurality of measuring positions for at least one sample and at least one reference. Hitherto, MEMS sensors have been primarily used in research laboratories. This use has made it possible to indicate the suitability of such MEMS sensors for thermal analytical processes and methods and has enabled improvements in sensor design.
A MEMS-based sensor, here also designated as a MEMS sensor, is suitable for the analysis of temperature-dependent phenomena of very small samples on account of its dimensions and thermal properties, and also enables very rapid heating and/or cooling rates compared to currently commercially available devices, as the components to be temperature controlled and also the sample have small thermal masses. A. W. van Herwaarden for example gives an overview of the use of different MEMS sensors as calorimeters for the analysis of very thin films and samples with masses in the microgram or even nanogram range in “Overview of calorimeter Chips for Various Applications”, Thermochimica Acta, 432 (2005), 192-201.
Research devices with MEMS sensors are typically not suitable for commercial use, where the user generally expects high reproducibility as well as reliability of the measurement results, a short time expenditure per measurement, and also user-friendly handling. Further, open systems are typically used in a research laboratory, which allows the experimenter to intervene into the experiment set-up at any time in order to optimize the same or to adapt the same to a planned experiment.
In research, it has proven beneficial if the sample for investigation or measurement is applied directly onto the sensor. The investigation of temperature phenomena of the sample can also lead to the sample fusing with the sensor. Therefore, changing a sample can be associated with an exchange of the sensor.
For commercial devices direct intervention into the experiment set-up by means of the user is generally excluded or at least severely restricted in order to increase the user friendliness of a device. A simple and fast sample change is also required, which is neither desired nor necessary for research devices.
In particular, when the sensors are operated in the low temperature range, various problems can arise, such as for example condensation water formation or icing up of individual components or the entire device as a consequence of repeated heating/cooling cycles. Especially in relation to a commercial device, it is desirable to prevent condensation water formation, the penetration of condensation water into the device (above all into the electronics), and in particular icing up, in order to eliminate the arising of artifacts to the greatest extent possible. In addition, it is desirable if the downtimes or defrost times between two measurements is as short as possible and thus the sample throughput can be kept high.
The provision of a commercially usable thermal analysis device that can provide a stable and reproducible measurement behavior is, therefore, desirable. Preferably, such a device has a compact construction, allows for simple handling, in particular when exchanging or replacing the sensor, and requires only a short time expenditure per measurement.